Colloid-chemical studies with nickel and chromium soaps in organic solvents

Summary Viscometric, spectrophotometric and solubility measurements have been made to study the colloidchemical behaviour of chromium and nickel soaps (stearate, palmitate, myristate and laurate) in a number of organic solvents. The experimental results have been sucessfully employed to determine the c.m.c. and the concentration of these metal soaps. Nickel stearate has been found to undergo thixotropic gelation in toluene.     

Speciation studies of nickel and chromium in wastewater from an electroplating plant

A speciation scheme involving the use of flame atomic absorption spectrometry (FAAS) and differential pulse adsorptive cathodic stripping voltammetry (DPAdCSV) techniques was applied to studies of nickel and chromium in wastewater from a nickel-chrome electroplating plant. Dimethylglyoxime (DMG) and diethylenetriaminepentaacetic acid (DTPA) were employed as complexing agents for adsorptive voltammetric determination of Ni and Cr, respectively. Cr(III) and Cr(VI) were determined by exploiting differences in their reactivity towards DTPA at HMDE. Total dissolved metal content was in the range 2906-3141 and 30.7-31.2 mg l⁻¹ for Ni and Cr, respectively. A higher percentage of the metal was present as labile species (mean value of 67.9% for Ni and 79.8% for Cr) suggesting that strongly binding ligands are not ubiquitous in the sample. About 77.8% of Cr was found to exist in the higher oxidization state, Cr(IV). Results on effect of dilution on lability of the metal forms in the sample using DPAdCSV showed slight peak shifts to a more negative (cathodic) value by −0.036 V for Ni and −0.180 V for Cr with a dilution factor of 100, while peak intensity (cathodic current) remained fairly constant.     

DTA and X-ray diffraction investigations of laser-irradiated CeO2 powders

The TG and DTA curves and diffractograms of powdered CeO₂ samples irradiated with a CO₂ laser beam with powers of 0.41–1.39 kW/cm² are presented. The laser treatment induced structural changes and probably generation of a metastable phase. X-ray diffraction coupled with thermal analysis was used to establish the structural modifications in the irradiated samples after heating.     

DTA studies on the corrosion behavior of titanium powder in NaCl and Na2SO4

The corrosion/oxidation behavior of titanium powder in air and in the presence of corrodents NaCl and Na₂SO₄ was investigated by employing the DTA technique.The DTA results for pure and fine titanium powder in air indicate two high-temperature exotherms, one at 700° and the other at around 750°. The first exotherm is due to the formation of anatase (TiO₂) and the second to rutile (TiO₂), as evidenced by the XRD data. However, the presence of NaCl and Na₂SO₄ promote the direct oxidation of titanium to rutile, which is indicated by a large exotherm ranging between 600 and 850°. The endotherm at 690° for mixtures containing 25 to 30% NaCl to Na₂SO₄ corresponds to formation of the eutectic mixture. The DTA data clearly indicate that the presence of the corrodents not only lowers the temperature of oxidation, but also induce the catastrophic oxidation of titanium powder.

---

Zusammenfassung Mittels DTA-Techniken wurde das Korrosions-/Oxydationsverhalten von Titanpulver an Luft und in Gegenwart von NaCl und Na₂SO₄ untersucht.Die DTA-Ergebnisse für reines, feines Titanpulver zeigen bei 700° und bei etwa 750° zwei Hochtemperaturexothermen. Wie durch Röntgendiffraktionsangaben bestätigt, gehört die erste Exotherme zur Bildung von Anatas (TiO₂), die zweite zur Bildung von Rutil (TiO₂). In jedem Falle begünstigt die Gegenwart von NaCl und Na₂SO₄ die direkte Oxydation von Titanpulver zu Rutil, was durch eine breite Exotherme im Bereich von 600–850° angezeigt wird. Der Endothermen bei 690° bei Gemischen mit einem Gehalt an 25–30% NaCl oder Na₂SO₄ liegt die Bildung von eutektischen Gemischen zugrunde. Die DTA-Daten zeigen eindeutig, daß die Wirkung der korrodenten Zusätze nicht nur in einer Herabsetzung der Oxydationstemperetur, sondern auch in einem eindeutigen Vorantrieb der Oxydation besteht.

---

---

The author thanks Dr. P. Rama Rao, Director, DMRL, for his encouragement and permission to publish these research findings; he also expresses thanks to the XRD, AES, and chemical analysis group for their help, and to Mr. M. Hema Reddy for supplying the DTA specimen holders.     

The electric conductivity of mixed copper and nickel powders

The electric conductivity of compressed mixtures of dendritic copper powder and carbonyl nickel has been measured in the pressure range of 4 … 200 MPa (about 40 … 2000 atmospheres) at ambient temperatures. The pure copper powders shows the well-known behaviour of smooth metal, covered with very thin, brittle, insulating layers. At low pressure, the powder mixtures can be described by percolation theory or similar hypotheses. Above 15 MPa (about 150 atmospheres) straight logarithmic mixing rules have been found. The conductivity of pure carbonyl nickel can be described by a uniform pressure exponent α ∼ 0.88. A new type of deviations from Ohm's law has been found, which occurs at low electric field strength.     

The preparation of organically functionalized chromium and nickel nanoparticles

Nanoparticles of chromium or nickel have been prepared by the reduction of either CrCl2 or Ni(acac)2 (acac = pentane-2,4-dionate) at elevated temperatures in various Lewis base solvents; the effect of the Lewis base, which acts as both a reaction solvent and passivating ligand on morphology are apparent; the nanostructures have been analysed by NMR, IR, TEM and XRD.     

A TG/DTA/MS study of the oxidation of nickel sulphide

The oxidative behaviour of synthetic millerite (Ni_0.994S) has been studied by TG and DTA in a dynamic oxygen atmosphere (0.2 l min^–1) over the temperature range 20–1000° (heating rate 10° min^–1). EGA was carried out by a coupled mass spectrometer. The reaction products at various intermediate temperatures were characterized by X-ray powder diffractometry. A reaction sequence has been deduced, in which in the temperature range 550–700° complete oxidation of Ni_0.994S had occurred with the formation of NiSO₄, Ni₃S₂, NiO and possibly-Ni₇S₆. Between 700–800°, NiSO₄ continued to be formed, whilst Ni₃S₂ and-Ni₇S₆ were oxidised. Above 800°, NiSO₄ decomposed to NiO, the latter being the only species evident above 800°.

---

Zusammenfassung Das oxidative Verhalten von synthetischem Millerit (Ni_0.994S) wurde mittels TG und DTA in einer dynamischen Sauerstoffatmosphäre (0.2 l min^–1) im Temperaturbereich von 20 bis 1000° (Aufheizgeschwindigkeit 10° min^–1) untersucht. EGA wurde mit einem gekoppelten Massenspektrometer durchgeführt. Die Reaktionsprodukte bei verschiedenen Zwischentemperaturen wurden mittels Röntgen-Pulver-Diffraktometrie charakterisiert. Eine Reaktionssequenz wurde abgeleitet, nach welcher im Temperaturbereich von 550 bis 700° die vollständige Oxidierung von Ni_0.994S unter Bildung von NiSO₄, Ni₃S₂, NiO und wahrscheinlich-Ni₇S₆ vor sich geht. Zwischen 700 und 800° wird NiSO₄ auch weiterhin gebildet, während Ni₇S₂ und-Ni₇S₆ oxidiert wurden. Oberhalb von 800° wurde NiSO₄ zu NiO zersetzt, das einzig nachweisbare Produkt oberhalb von 800°.

---

Résumé On a étudié l'oxydation de la millérite synthétique (Ni_0.994S) par TG et ATD en atmosphère dynamique d'oxygène (0,2 1· min^–1) et dans l'intervalle de températures allant de 20 à 1000° (vitesse de chauffage 10°· min^–1). L'analyse des gaz émis s'est effectuée avec un spectromètre de masse couplé. Les produits de réaction ont été caractérisés à diverses températures intermédiaires par diffractométrie de poudre aux rayons X. On a déduit une séquence de réactions, selon laquelle, dans l'intervalle compris entre 550 et 700°, l'oxydation complète de Ni_0.994S a lieu avec formation de NiSO₄, Ni₃S₂, NiO et probablement-Ni₇S₆. Entre 700 et 800°, la formation de NiSO₄ se poursuit tandis que Ni₃S₂ et-Ni₇S₆ sont oxydés. Au-dessus de 800°, NiSO₄ se décompose en NiO qui constitue l'unique composé qui puisse être décelé au-dessus de 800°.

---

(Ni_0.994S) (0,2 . ^–1) 20–1000° 10° ^–1. - . . 550–700° Ni_0.994S NiSO₄, Ni₃S₂, NiO -Ni₇S₆. 700–800° , Ni₃S₂ -Ni₇S₆ . 800° NiO, 800°.

---

---

We wish to thank Dr. T. Kennedy for useful discussions and Messrs. B. Sturman, I. Twaddle, K. Oliver and W. Thomas for technical assistance.     

The Piloyan method in DTA studies of glass devitrification

A kinetic analysis of the applicability of the Piloyan method to the process of glass devitrification for evaluation of the exponentn in the Johnson-Mehl-Avrami equation is carried out.Criado's conclusions concerning the value of the slope of the Piloyan plot are criticized.     

The kinetics and mechanism of mechanochemical dissolution of chromium in nickel

The regularities of the formation of a solid solution in a Ni-Cr(20 at %) system are studied using X-ray diffraction, optical microscopy, and particle-size distribution analysis within the framework of an energetical approach to the analysis of the kinetics of mechanochemical synthesis. It is established that the curves of the consumption of chromium atoms and the formation of the reaction product (a solid solution of chromium in nickel) coincide with each other. The rate-limiting step of the reaction is the formation of a contact surface between chromium and nickel, while the “stirring” of chromium atoms in nickel matrix has a very high rate. The rate of the formation of the contact surface in the mixture of brittle chromium and plastic nickel is determined by the rate of chromium particle disintegration. To a conversion of about 60%, the reaction kinetics is described by a quadratic dependence on the dose (D) of the mechanical treatment (N ～ D ₂).     

Speciation of chromium,lead and nickel compounds by laser microprobe mass spectrometry and application to environmental and biological samples

Laser microprobe mass spectrometry with time-of-flight analyser is evaluated as a tool to perform speciation of chromium, nickel and lead compounds in solids with a lateral resolution in the μm range. Commercial instruments irradiate the sample at 266 nm while a tunable dye laser is fitted to some experimental set-ups. The analytical merits of both approaches are surveyed and their application to selected test cases in the field of environment and biological tissue analysis at the sub-cellular level is presented. A comparison between TOF LMMS and μ-Raman for the speciation of given components in large industrial airbone particles is discussed.     

The colorimetric determination of nickel,chromium, and manganese in steel

With the aid of the Spckkei absorptiometer the colonmetnc delerminations, of nickel (with dimethylglyoxime), chromium (with diphenylcarbazide) and manganese (after oxidation with periodate) in steel were critically sinveyed The following factors were examined. wave length of the light, concentration of the reagents, stability of the coloured solution, temperature, influence of excess non, relation of extinetion coefficient and concentration of the coloured solution, influence of Mo, V, W, Ti, Al, Co, Cu, Ni, Cr, Mn, P and Si.For each determination a recommended procedure is given, with the results of control analyses. The recommended procedures are rapid. They can be used with steels of widely differing composition. The methods are accurate within 5% of the actual Value. 1. NickleAfter neutrahsing the solution 5 ml (01 more) of concentrared ammonia (0.95) must be added. The temperature of the solution must be kept below 30° C before adding the dimethylglyoxime.The extinction coefficient is determined with light of 520 m/gm 2. ChromiumThe chromium is oxidised with hydrogen peroxide in alkaline solution. The influence of iron is ehminated by the addition of phosphoric acid. The recommended acidity is o.2 n, the quantily of diphenylcarbazide is 2 ml of a 1%'s solution in aceton. The determinations are made with a mercury lamp and filter (546 m/gm) 3. ManganeseThe solution of the sampie is boiled with ammoniumpersulphate and then oxidised with 300–500 mg of potassium periodate.The recommended acidity is 2 n, using a mixture of equal parts of sulphuric and phosphoric acids. The determinations are made with light of 520 m/gm.     

Spectrophotometric determination of vanadium(V) and its application to vanadium steel containing chromium,molybdenum, manganese,and nickel

Promethazine hydrochloride forms a red colored species with vanadium(V) in 6.0–7.5 M phosphoric acid. A 16-fold molar excess of the reagent is necessary for full development of color intensity. Beer's law is valid over the concentration range of 0.1–7.0 ppm. The optimum concentration range as evaluated by Ringbom's method is 0.5–7.0 ppm. The sensitivity of the reaction is 0.005 μg cm^?2 and the molar absorptivity is 9.60 × 10³ liter mol^?1 cm^?1 at 517 nm. The effects of acidity, time, temperature, order of addition of reagents, reagent concentration, and the interferences from various ions were reported. Vanadium in vanadium steel containing chromium, molybdenum, manganese, and nickel was determined.     

Application of DTA and TG to studies of the CaCO3-CaF2 phase diagram

A new method (based on DTA and TG) for the determination of the eutectic composition is proposed for systems in which one of the components is unstable in the vicinity of the eutectic melting temperature. The eutectic composition established by means of this method for the CaCO₃-CaF₂ system is in very good agreement with the results obtained in a classical way.

---

Zusammenfassung Eine neue Methode zur Bestimmung der eutektischen Zusammensetzung von Systemen, deren eine Komponente in der Nähe der eutektischen Temperatur instabil ist, beruht auf der simultanen TG-Messung. Mit der vorgeschlagenen Methode wird die eutektische Zusammensetzung des Systems CaF₂-CaCO₃ in sehr guter Übereinstimmung mit den Ergebnissen klassischer Untersuchungen gefunden.

---

, . , CaCO₃-CaF₂, , .

     

Location of chromium and nickel cations in stabilized Y zeolites

The influence of the hydrothermal treatment of stabilized and nonstabilized Y zeolites on the location of Cr and Ni cations was tested. A significant influence of the above treatment was found.

---

Cr Ni. .

     

Identification of chromium and nickel sites in zinc phosphate glasses

Optical and EPR investigations of chromium and nickel doped zinc phosphate glasses are carried out at room temperature to evaluate crystal field, spin-Hamiltonian and bonding parameters. For Cr³⁺ ion, the site symmetry is ascribed to a distorted octahedron, whereas the Ni²⁺ ion is located in a near octahedral site. In addition, the bonding parameters suggest covalent nature for Cr³⁺ and a moderate covalent nature for Ni²⁺ in the zinc phosphate glasses.     

Thermal properties and reactivity determination of micro- and submicrometer nickel powders

Monodispersed fine metal nickel powders of uniform shape and high purity are increasingly required for specific uses in many technological areas, especially in the preparation of electronic materials such as the manufacture of conductive inks and pastes and the formation of catalysts. Metallic nickel powders were prepared in ethylene glycol by the reduction of a nickel solution. Hydrazine was used as a reducing agent. Metal powders were characterized by chemical analysis, scanning electron microscopy (SEM), thermogravimetry (TG), derivative thermogravimetry (DTG) and differential scanning calorimetry (DSC). Particle size distributions were determined using laser light scattering. The reactivity and purity of these fine nickel powders were tested by repeated oxidation and reduction of nickel powders in oxidative and reductive atmospheres.     

Slurry-based procedures to determine chromium, nickel and vanadium in complex matrices by ETAAS

Two slurry-based ETAAS methodologies are compared to determine directly Cr, Ni and V in coal fly ash, soils and sediments: current slurry analysis (USS) and ‘slurry extraction’ (SE). Slurries for USS-ETAAS were prepared in 0.5% HNO₃. HF and HNO₃ were evaluated as chemical modifiers. HF was the extractant for the SE-ETAAS approach.A unique slurry-based procedure to measure Cr, Ni and V could not be established. Cr concentrations up to 100 μg g^{− 1} were accurately determined by USS (0.5% HNO₃; λ = 429.0 nm; LOD = 0.35 μg g^{− 1}) whereas higher contents required the SE procedure (sample grinding, 30% HF; LOD = 0.02 μg g^{− 1}). Both methods were appropriate to determine Ni (LOD = 0.11 and 0.08 μg g^{− 1}, for USS and SE, respectively). V was satisfactorily quantified only with the USS approach (LOD = 0.80 μg g^{− 1}).     

片状镍粉的制备及其磁性研究

利用湿法研磨法由微米镍粉制得了不同尺寸的片状镍粉;利用X射线衍射仪和扫描电子显微镜研究了研磨参数对片状镍粉形貌和微观结构的影响;测定了产物的室温磁性能.结果表明,球料比和研磨时间是影响片状镍粉形貌的关键因素,片状镍粉的剩磁比和矫顽力都比原料微米镍粉的高.所采用的制备方法具有效率高、成本低且产物形状及磁性能可控的特点,适...     

Interfacial oxidation of ultrathin nickel and chromium films on yttria-stabilized zirconia

The substrate-induced oxidation upon prolonged annealing in UHV of ultrathin films of Ni and Cr vapor deposited on yttria-stabilized zirconia YSZ(100) was studied by X-ray photoelectron spectroscopy (XPS) to obtain information about the oxidation mechanism, determine the available quantity of reactive oxygen in YSZ, and investigate the thermal stability of the thin oxide films. Up to about 0.8 ML of Ni deposited at room temperature was oxidized to NiO at a constant rate at 650 K via the substrate, whereas at slightly higher coverage, the oxidation rate under identical conditions was drastically reduced. In contrast to Ni, up to 4.8 ML of Cr deposited at 275 K could be oxidized via the substrate to Cr2O3 upon extensive UHV annealing at increasing temperature up to 820 K, indicating a reactive oxygen content of at least 4 x 10(-6) with respect to the lattice oxygen in the YSZ specimen. The Cr2O3 decomposed to metallic Cr above about 800 K, whereas NiO was stable up to the maximum temperature of 875 K. These results indicate that the oxidation via the substrate is kinetically analogous to the gas-phase oxidation of bulk Ni and Cr. The reactive oxygen content of the single-crystal YSZ is larger than expected, and part of it is accommodated at the surface of the substrate. The thermal stability of the thin oxide films is determined by the oxygen exchange with YSZ and not by the respective bulk oxide thermodynamic decomposition temperature.